1. Field of the Invention
The present invention relates to a semiconductor device, and more particularly, to a semiconductor device such as a discrete transistor, a metal oxide semiconductor (MOS) device and an integrated circuit of a structure having a breakdown voltage structure between two electrodes of a transistor.
2. Description of the Prior Art
Generally, in an input transistor, a Zener diode is connected between two electrodes to protect the transistor from a surge voltage. In a bipolar transistor, as shown in FIG. 1, a Zener diode ZD having a predetermined breakdown voltage is connected between a base B and a collector C. In a MOS transistor, as shown in FIG. 2, Zener diodes ZDa and ZDb having a predetermined breakdown voltage are connected between the gate G and the source S. In FIG. 2, the diodes ZDa and ZDb are connected to be of back-to-back polarity.
These Zener diodes are formed to have a specific breakdown voltage such as 5 V, 15 V, 30 V and 90 V according to the purpose of the transistor. While the Zener diodes are ordinarily formed within an integrated circuit chip in an integrated circuit, in a discrete transistor, Zener diodes are frequently formed on the semiconductor substrate together with the transistor.
When a semiconductor device is incorporated in a television receiver set, if heat is not released in the semiconductor device because of defective heat release, the breakdown voltage of the Zener diode is changed. For example, the breakdown voltage of a Zener diode designed to have a breakdown voltage of 30 V is increased to 40 V when the temperature increases, so that a transistor cannot sufficiently be protected from a surface voltage of from 30 V to 35 V. As a result, a problem is caused in the operation of the receiver set.